Method for manufacturing metal electrode having transition metallic coating layer and metal electrode manufactured thereby

ABSTRACT

It is to provide a method for manufacturing a metal electrode having transition metal oxide coating layer and a metal electrode manufactured thereby, which eliminates a contact resistance problem and simultaneously improves electric conductivity of the electrode by using a one body electrode, which is not requiring separate current collector and binder, and further maintains pseudo-capacitance from the redox reaction by coating the metal surface with a transition metal oxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 12/511,806filed on Jul. 29, 2009, which claims the benefit of Korean PatentApplication No. 10-2009-0020314 filed with the Korean IntellectualProperty Office on Mar. 10, 2009, the disclosures of which areincorporated herein by reference.

BACKGROUND

1. Technical Field

It relates to a method for manufacturing a metal electrode having atransition metal oxide coating layer and a metal electrode manufacturedthereby.

2. Description of the Related Art

Higher value-added businesses which collect and use various and usefulinformation in real time by employing IT equipments receive attentionsand stable energy supply for securing reliability of such systemsbecomes an important factor in the information-oriented society. TheseIT equipments and electrical devices include electric circuit boards andeach circuit board has a capacitor which stores an electric charge andreleases it when required and thus stabilizes energy flow in thecircuit. This capacitor has a very short charge/discharge time, a longlifetime and a high power density but generally a very low energydensity. This disadvantage of low energy density causes many limitationson its use as an energy storage device.

However, electrochemical capacitors, supercapacitors or ultracapacitors,which have started to be commercialized in Japan, Russia, USA, etc.since 1995, are under development in all countries of the world toprovide higher energy density as next generation energy storage devicesalong with secondary batteries.

A supercapacitor can be broadly classified into 3 categories dependingon the electrode and the mechanism: (1) an electric double layercapacitor(EDLC) which employs activated carbon as an electrode and isbased on an electric double layer electric charge absorption mechanism;(2) a metal oxide electrode pseudocapacitor(or redox capacitor) whichemploys a transition metal oxide and a conductive polymer as anelectrode material and is based on a pseudo-capacitance mechanism; and(3) a hybrid capacitor which combines the features of bothelectrochemical and electrolytic capacitors. Among them, the EDLC-typesupercapacitor using activated carbons is currently used the most.

The supercapacitor is composed of an electrode, an electrolyte, acurrent collector, and a separator and is based on the electrochemicalmechanism which stores energy through absorption of electrolyte ions onthe electrode surface by migrating along with the electric field whenvoltages are applied on the both ends of a unit cell electrode. Sincethe specific capacitance is proportional to the specific surface area,the supercapacitor improves energy(storage) density through the use ofan activated carbon electrode, which is a porous material. An electrodeis manufactured by preparing slurry including a carbon electrodematerial, a carbon conductive material and a polymer binder and coatingthe slurry on a current collector. Here, it is important to improveadhesiveness to the current collector and reduce contact resistance atthe same time and further lower internal contact resistance betweenactivated carbons by changing a ratio or kind of the binder, theconductive material and the electrode material.

When a pseudocapacitor using a metal oxide electrode material is used,the transition metal oxide exhibits higher capacity and higher powerdensity compared to activated carbons. Recently, it has been reportedthat amorphous hydrate electrodes exhibit much higher specificcapacitance.

Since the electric capacitance is proportional to the specific surfacearea, it is needed to use an electrode material having high specificsurface which is the most essential factor to improve a capacitance of asupercapacitor. In addition, it is needed to have high conductivity,electrochemical inactivity, easy forming and processability and thelike. Carbon materials which satisfy such properties have been widelyused the most. Examples of such porous carbon materials may includeactivated carbon, activated carbon fiber, amorphous carbon, carbonaerogel or carbon carbon composite, carbon nanotube and the like.However, even though such activated carbons have high specific surfacearea, effective pores of the activated carbon are only about 20% becausemost pores are micropores of which diameter is about 20 nm or less andwhich cannot do much for an electrode role. Since the electrode isprepared from slurry which is formed by mixing a binder, a carbonconducting material and a solvent, etc. an actual effective contact areabetween an electrode and an electrolyte is decreased. There are furtherdrawbacks such as uneven electric capacitance and contact resistancebetween an electrode and a current collector.

KR patent application no. 2003-0099761 discloses a method formanufacturing an electrode for supercapacitors by using a metal oxide,instead of using a binder, to increase effective contact area but itstill has drawbacks such as low conductivity, contact resistance andhigh manufacturing cost, etc.

SUMMARY

It is to provide a method for manufacturing a metal electrode forsupercapacitors having a transition metal oxide coating layer on thesurface and optimizing surface area in which the metal electrode is onebody electrode since a current collector and a binder are not separatelyused, and a metal electrode manufactured thereby.

There is an aspect to provide a method for manufacturing a metalelectrode having a transition metal oxide coating layer including:preparing an anode aluminum oxide template or polymer casting moldhaving more than two micropores; forming a metal substrate by sputteringa first metal at one side where the opening parts of the micropores ofthe aluminum template or the polymer casting mold are; forming more thantwo metal nanowire arrays by filling a second metal into the microporesof the aluminum template or the polymer casting mold by using anelectroplating method; exposing the metal nanowire arrays arrangedperpendicularly on the metal substrate by removing the aluminum templateor the polymer casting mold; and coating the side, where the metalnanowire arrays are perpendicularly arranged on the metal substrate, andthe side, where the metal nanowire arrays are exposed, with a transitionmetal oxide by an immersion method.

According to an embodiment, the the first metal and the second metal maybe identical.

According to an embodiment, the first metal and the second metal may beindependently chosen from Cu, Ag, Au, Ni, Cr, Sn, Cd, Pb, Rd, Pt, Pd,In, Ru, Mn, Zn, Co and an alloy thereof.

According to an embodiment, the transition metal oxide may be chosenfrom MnO₂, RuO₂, CoO and NiO.

There is another aspect to provide a metal electrode having a transitionmetal oxide coating layer manufactured by the method described above.

There is still another aspect to provide a metal electrode including: ametal substrate composed of a first metal; more than two metal nanowirearrays arranged perpendicularly on the metal substrate and composed of asecond metal; and a transition metal oxide coating layer coated on theside where the metal nanowire arrays are arranged on the metal substrateand the side where the metal nanowire arrays are exposed.

According to an embodiment, the the first metal and the second metal maybe identical. When they are identical, a one body metal electrode may beobtained.

According to an embodiment, the first metal and the second metal may beindependently chosen from Cu, Ag, Au, Ni, Cr, Sn, Cd, Pb, Rd, Pt, Pd,In, Ru, Mn, Zn, Co and an alloy thereof.

According to an embodiment, the transition metal oxide may be chosenfrom MnO₂, RuO₂, CoO and NiO.

There is still another aspect to provide a supercapacitor including themetal electrode described above.

According to an embodiment, the metal electrode, manufactured by theabove described method, eliminates a contact resistance problem andsimultaneously improves electric conductivity of the electrode by usinga one body electrode, which is not requiring separate current collectorand binder, and further maintains pseudo-capacitance from the redoxreaction by coating the metal surface with a transition metal oxide. Inaddition, the metal electrode may have superior power density, which hasa high effect on supercapacitor's characteristics, to conventional onessince a metal itself is used as an electrode and thus the electricconductivity of the metal has 10⁹ times better than that of the metaloxide.

Further, the surface area of the electrode may be optimized by formingmore than two metal nanowire arrays with using an anode aluminum oxidetemplate or polymer casting mold. Here, diameters of the metal nanowirearrays may be controlled by controlling diameters of micropores of theanode aluminum oxide template or polymer casting mold. Lengthes of themetal nanowire arrays may be also controlled by controllingelectrochemical parameters such as supplied current density and supplingtime, etc. during the electroplating process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method for manufacturing a metal electrodeaccording to an embodiment.

FIG. 2 is an enlarged sectional view of a part of an metal electrodemanufactured by an embodiment.

DETAILED DESCRIPTION

Hereinafter, a metal electrode having a transition metal oxide coatinglayer according to an embodiment and a manufacturing method thereof willbe described in more detail.

As illustrated in FIG. 1, a method for manufacturing a metal electrodehaving a transition metal oxide coating layer according to an embodimentmay include (a) preparing an anode aluminum oxide template or polymercasting mold 10 having more than two micropores; (b) forming a metalsubstrate 20 by sputtering a first metal at one side where the openingparts of the micropores of the aluminum template or the polymer castingmold are; (c) forming more than two metal nanowire arrays 30 by fillinga second metal into the micropores of the aluminum template or thepolymer casting mold by using an electroplating method; (d) exposing themetal nanowire arrays arranged perpendicularly on the metal substrate byremoving the aluminum template or the polymer casting mold; and (e)coating 40 the side, where the metal nanowire arrays are arranged on themetal substrate, and the side, where the metal nanowire arrays areexposed, with a transition metal oxide by an immersion method.

In step (a), the anode aluminum oxide template (AAO) or polymer castingmold, formed with more than two micropores having several tens toseveral hundreds nanometer of a diameter, is prepared.

Manufacturing the anode aluminum oxide template (AAO) or polymer castingmold formed with more than two micropores and controlling size ofmicropores may be carried by any method well-known in this field andthus detail description is omitted. The casting mold may have 20 nm to200 nm of a diameter.

In step (b), the metal substrate may be formed by sputtering a firstmetal on one side where the opening parts of the micropores of thecasting mold are.

The first metal may be chosen from Cu, Ag, Au, Ni, Cr, Sn, Cd, Pb, Rd,Pt, Pd, In, Ru, Mn, Zn, Co and an alloy thereof. The first metal may beformed as a metal layer to function as a substrate so that it is able toarrange more than two metal nanowire arrays perpendicularly. This metalsubstrate may function as a current collector at the same time byconnecting the more than two metal nanowire arrays.

In step (c), the more than two metal nanowire arrays 30 may be formed byfilling a second metal into the micropores of the casting mold by usingan electroplating method.

The second metal may be chosen from Cu, Ag, Au, Ni, Cr, Sn, Cd, Pb, Rd,Pt, Pd, In, Ru, Mn, Zn, Co and an alloy thereof. The first and secondmetal may be identical. When the electroplating is carried by placingthe casting mold to an electroplating solution, the second metal isfilled into the micropores through the opening parts of those microporesof the casting mold and thus the metal nanowire array can be formed.

In step (d), the metal metal nanowire arrays arranged perpendicularlymay be exposed on the metal substrate by removing the aluminum orpolymer casting mold.

The aluminum or polymer casting mold may be removed by an etchingtreatment in an etching solution which is able to dissolve the castingmold.

In step (e), the transition metal oxide coating layer may be formed bycoating the side where the metal nanowire arrays are arrangedperpendicularly on the metal substrate and the side where the metalnanowire arrays are exposed by the immersion method.

The transition metal oxide may be chosen from MnO₂, RuO₂, CoO, NiO andthe like.

A metal electrode manufactured by the method for manufacturing a metalelectrode having a transition metal oxide coating layer according to anembodiment may include: a metal substrate composed of a first metal;more than two metal nanowire arrays arranged perpendicularly on themetal substrate and composed of a second metal; and a transition metaloxide coating layer coated on the side where the metal nanowire arraysare arranged on the metal substrate and the side where the metalnanowire arrays are exposed.

The metal electrode may be suitable for supercapacitors by being used asan anode, a cathode, or both electrodes. A supercapacitor according toan embodiment may optimize an effective contact area between anelectrolyte and an active material to increase capacitance and improve arate for charge/discharge process of a capacitor due to easy iondiffusion. It also eliminates a contact resistance since a currentcollector and an electrode is a single body.

Hereinafter, although more detailed descriptions will be given byexamples, those are only for explanation and there is no intention tolimit the invention.

EXAMPLE

1) An anode aluminum oxide template(AAO template) having more than twomicropores with 20-200 nm of a diameter was prepared.

2) A copper substrate having 1-50 μm of thickness was formed on one sidewhere the opening parts of the micropores of the template are by using asputtering apparatus.

3) The anode aluminum oxide template having the copper substrate formedon one side and the opening parts of the micropores on the one side wasperformed for the electroplating by placing into a copper electroplatingsolution and supplying current to fill copper into the micropores.

4) The template formed with the copper nanowire array was immersed intoa 0.1 M to 5 M NaOH solution for 10 minutes to 1 hour to remove thealuminum mold and dried to expose the copper nanowire array.

5) The side, where the copper nanowire arrays arranged perpendicularlyon the copper substrate were exposed, was coated with MnO₂ by theimmersion method to form a transition metal oxide coating layer. Anelectrode having the transition metal oxide coating layer wasmanufactured as in FIG. 2.

While it has been described with reference to particular embodiments, itis to be appreciated that various changes and modifications may be madeby those skilled in the art without departing from the spirit and scopeof the embodiment herein, as defined by the appended claims and theirequivalents.

1-4. (canceled)
 5. A metal electrode having a transition metal oxidecoating layer manufactured according to a method for manufacturing ametal electrode having a transition metal oxide coating layercomprising: preparing an anode aluminum oxide template or polymercasting mold having more than two micropores; forming a metal substrateby sputtering a first metal at one side where the opening parts of themicropores of the aluminum template or the polymer casting mold are;forming more than two metal nanowire arrays by filling a second metalinto the micropores of the aluminum template or the polymer casting moldby using an electroplating method; exposing the metal nanowire arraysarranged perpendicularly on the metal substrate by removing the aluminumtemplate or the polymer casting mold; and coating the side where themetal nanowire arrays are arranged on the metal substrate and the sidewhere the metal nanowire arrays are exposed with a transition metaloxide by an immersion method.
 6. A metal electrode comprising: a metalsubstrate composed of a first metal; more than two metal nanowire arraysarranged perpendicularly on the metal substrate and composed of a secondmetal; and a transition metal oxide coating layer coated on the sidewhere the metal nanowire arrays are arranged on the metal substrate andthe side where the metal nanowire arrays are exposed.
 7. The metalelectrode of claim 6, wherein the first metal and the second metal areidentical.
 8. The metal electrode of claim 6, wherein the first metaland the second metal are independently selected from the groupconsisting of Cu, Ag, Au, Ni, Cr, Sn, Cd, Pb, Rd, Pt, Pd, In, Ru, Mn,Zn, Co and an alloy thereof.
 9. The metal electrode of claim 6, whereinthe transition metal oxide oxide is selected from the group consistingof MnO₂, RuO₂, CoO and NiO.
 10. A supercapacitor comprising the metalelectrode of claim
 5. 11. A supercapacitor comprising the metalelectrode of claim 6.